/*
** SGI FREE SOFTWARE LICENSE B (Version 2.0, Sept. 18, 2008)
** Copyright (C) [dates of first publication] Silicon Graphics, Inc.
** All Rights Reserved.
**
** Permission is hereby granted, free of charge, to any person obtaining a copy
** of this software and associated documentation files (the "Software"), to deal
** in the Software without restriction, including without limitation the rights
** to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
** of the Software, and to permit persons to whom the Software is furnished to do so,
** subject to the following conditions:
**
** The above copyright notice including the dates of first publication and either this
** permission notice or a reference to http://oss.sgi.com/projects/FreeB/ shall be
** included in all copies or substantial portions of the Software.
**
** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
** INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
** PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL SILICON GRAPHICS, INC.
** BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
** TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
** OR OTHER DEALINGS IN THE SOFTWARE.
**
** Except as contained in this notice, the name of Silicon Graphics, Inc. shall not
** be used in advertising or otherwise to promote the sale, use or other dealings in
** this Software without prior written authorization from Silicon Graphics, Inc.
*/
/*
** Author: Eric Veach, July 1994.
*/

//#include "tesos.h"
#include <stddef.h>
#include <assert.h>
#include "mesh.h"
#include "geom.h"
#include "bucketalloc.h"

#define TRUE 1
#define FALSE 0

/************************ Utility Routines ************************/

/* Allocate and free half-edges in pairs for efficiency.
* The *only* place that should use this fact is allocation/free.
*/
typedef struct { TESShalfEdge e, eSym; } EdgePair;

/* MakeEdge creates a new pair of half-edges which form their own loop.
* No vertex or face structures are allocated, but these must be assigned
* before the current edge operation is completed.
*/
static TESShalfEdge *MakeEdge( TESSmesh* mesh, TESShalfEdge *eNext )
{
    TESShalfEdge *e;
    TESShalfEdge *eSym;
    TESShalfEdge *ePrev;
    EdgePair *pair = (EdgePair *)bucketAlloc( mesh->edgeBucket );
    if (pair == NULL) return NULL;

    e = &pair->e;
    eSym = &pair->eSym;

    /* Make sure eNext points to the first edge of the edge pair */
    if( eNext->Sym < eNext ) { eNext = eNext->Sym; }

    /* Insert in circular doubly-linked list before eNext.
    * Note that the prev pointer is stored in Sym->next.
    */
    ePrev = eNext->Sym->next;
    eSym->next = ePrev;
    ePrev->Sym->next = e;
    e->next = eNext;
    eNext->Sym->next = eSym;

    e->Sym = eSym;
    e->Onext = e;
    e->Lnext = eSym;
    e->Org = NULL;
    e->Lface = NULL;
    e->winding = 0;
    e->activeRegion = NULL;

    eSym->Sym = e;
    eSym->Onext = eSym;
    eSym->Lnext = e;
    eSym->Org = NULL;
    eSym->Lface = NULL;
    eSym->winding = 0;
    eSym->activeRegion = NULL;

    return e;
}

/* Splice( a, b ) is best described by the Guibas/Stolfi paper or the
* CS348a notes (see mesh.h).  Basically it modifies the mesh so that
* a->Onext and b->Onext are exchanged.  This can have various effects
* depending on whether a and b belong to different face or vertex rings.
* For more explanation see tessMeshSplice() below.
*/
static void Splice( TESShalfEdge *a, TESShalfEdge *b )
{
    TESShalfEdge *aOnext = a->Onext;
    TESShalfEdge *bOnext = b->Onext;

    aOnext->Sym->Lnext = b;
    bOnext->Sym->Lnext = a;
    a->Onext = bOnext;
    b->Onext = aOnext;
}

/* MakeVertex( newVertex, eOrig, vNext ) attaches a new vertex and makes it the
* origin of all edges in the vertex loop to which eOrig belongs. "vNext" gives
* a place to insert the new vertex in the global vertex list.  We insert
* the new vertex *before* vNext so that algorithms which walk the vertex
* list will not see the newly created vertices.
*/
static void MakeVertex( TESSvertex *newVertex,
                       TESShalfEdge *eOrig, TESSvertex *vNext )
{
    TESShalfEdge *e;
    TESSvertex *vPrev;
    TESSvertex *vNew = newVertex;

    if(vNew == NULL) return;

    /* insert in circular doubly-linked list before vNext */
    vPrev = vNext->prev;
    vNew->prev = vPrev;
    vPrev->next = vNew;
    vNew->next = vNext;
    vNext->prev = vNew;

    vNew->anEdge = eOrig;
    /* leave coords, s, t undefined */

    /* fix other edges on this vertex loop */
    e = eOrig;
    do {
        e->Org = vNew;
        e = e->Onext;
    } while( e != eOrig );
}

/* MakeFace( newFace, eOrig, fNext ) attaches a new face and makes it the left
* face of all edges in the face loop to which eOrig belongs.  "fNext" gives
* a place to insert the new face in the global face list.  We insert
* the new face *before* fNext so that algorithms which walk the face
* list will not see the newly created faces.
*/
static void MakeFace( TESSface *newFace, TESShalfEdge *eOrig, TESSface *fNext )
{
    TESShalfEdge *e;
    TESSface *fPrev;
    TESSface *fNew = newFace;

    if(fNew == NULL) return;

    /* insert in circular doubly-linked list before fNext */
    fPrev = fNext->prev;
    fNew->prev = fPrev;
    fPrev->next = fNew;
    fNew->next = fNext;
    fNext->prev = fNew;

    fNew->anEdge = eOrig;
    fNew->trail = NULL;
    fNew->marked = FALSE;

    /* The new face is marked "inside" if the old one was.  This is a
    * convenience for the common case where a face has been split in two.
    */
    fNew->inside = fNext->inside;

    /* fix other edges on this face loop */
    e = eOrig;
    do {
        e->Lface = fNew;
        e = e->Lnext;
    } while( e != eOrig );
}

/* KillEdge( eDel ) destroys an edge (the half-edges eDel and eDel->Sym),
* and removes from the global edge list.
*/
static void KillEdge( TESSmesh *mesh, TESShalfEdge *eDel )
{
    TESShalfEdge *ePrev, *eNext;

    /* Half-edges are allocated in pairs, see EdgePair above */
    if( eDel->Sym < eDel ) { eDel = eDel->Sym; }

    /* delete from circular doubly-linked list */
    eNext = eDel->next;
    ePrev = eDel->Sym->next;
    eNext->Sym->next = ePrev;
    ePrev->Sym->next = eNext;

    bucketFree( mesh->edgeBucket, eDel );
}


/* KillVertex( vDel ) destroys a vertex and removes it from the global
* vertex list.  It updates the vertex loop to point to a given new vertex.
*/
static void KillVertex( TESSmesh *mesh, TESSvertex *vDel, TESSvertex *newOrg )
{
    TESShalfEdge *e, *eStart = vDel->anEdge;
    TESSvertex *vPrev, *vNext;

    /* change the origin of all affected edges */
    e = eStart;
    do {
        e->Org = newOrg;
        e = e->Onext;
    } while( e != eStart );

    /* delete from circular doubly-linked list */
    vPrev = vDel->prev;
    vNext = vDel->next;
    vNext->prev = vPrev;
    vPrev->next = vNext;

    bucketFree( mesh->vertexBucket, vDel );
}

/* KillFace( fDel ) destroys a face and removes it from the global face
* list.  It updates the face loop to point to a given new face.
*/
static void KillFace( TESSmesh *mesh, TESSface *fDel, TESSface *newLface )
{
    TESShalfEdge *e, *eStart = fDel->anEdge;
    TESSface *fPrev, *fNext;

    /* change the left face of all affected edges */
    e = eStart;
    do {
        e->Lface = newLface;
        e = e->Lnext;
    } while( e != eStart );

    /* delete from circular doubly-linked list */
    fPrev = fDel->prev;
    fNext = fDel->next;
    fNext->prev = fPrev;
    fPrev->next = fNext;

    bucketFree( mesh->faceBucket, fDel );
}


/****************** Basic Edge Operations **********************/

/* tessMeshMakeEdge creates one edge, two vertices, and a loop (face).
* The loop consists of the two new half-edges.
*/
TESShalfEdge *tessMeshMakeEdge( TESSmesh *mesh )
{
    TESSvertex *newVertex1 = (TESSvertex*)bucketAlloc(mesh->vertexBucket);
    TESSvertex *newVertex2 = (TESSvertex*)bucketAlloc(mesh->vertexBucket);
    TESSface *newFace = (TESSface*)bucketAlloc(mesh->faceBucket);
    TESShalfEdge *e;

    /* if any one is null then all get freed */
    if (newVertex1 == NULL || newVertex2 == NULL || newFace == NULL) {
        if (newVertex1 != NULL) bucketFree( mesh->vertexBucket, newVertex1 );
        if (newVertex2 != NULL) bucketFree( mesh->vertexBucket, newVertex2 );
        if (newFace != NULL) bucketFree( mesh->faceBucket, newFace );
        return NULL;
    }

    e = MakeEdge( mesh, &mesh->eHead );
    if (e == NULL) return NULL;

    MakeVertex( newVertex1, e, &mesh->vHead );
    MakeVertex( newVertex2, e->Sym, &mesh->vHead );
    MakeFace( newFace, e, &mesh->fHead );
    return e;
}


/* tessMeshSplice( eOrg, eDst ) is the basic operation for changing the
* mesh connectivity and topology.  It changes the mesh so that
*    eOrg->Onext <- OLD( eDst->Onext )
*    eDst->Onext <- OLD( eOrg->Onext )
* where OLD(...) means the value before the meshSplice operation.
*
* This can have two effects on the vertex structure:
*  - if eOrg->Org != eDst->Org, the two vertices are merged together
*  - if eOrg->Org == eDst->Org, the origin is split into two vertices
* In both cases, eDst->Org is changed and eOrg->Org is untouched.
*
* Similarly (and independently) for the face structure,
*  - if eOrg->Lface == eDst->Lface, one loop is split into two
*  - if eOrg->Lface != eDst->Lface, two distinct loops are joined into one
* In both cases, eDst->Lface is changed and eOrg->Lface is unaffected.
*
* Some special cases:
* If eDst == eOrg, the operation has no effect.
* If eDst == eOrg->Lnext, the new face will have a single edge.
* If eDst == eOrg->Lprev, the old face will have a single edge.
* If eDst == eOrg->Onext, the new vertex will have a single edge.
* If eDst == eOrg->Oprev, the old vertex will have a single edge.
*/
int tessMeshSplice( TESSmesh* mesh, TESShalfEdge *eOrg, TESShalfEdge *eDst )
{
    int joiningLoops = FALSE;
    int joiningVertices = FALSE;

    if( eOrg == eDst ) return 1;

    if( eDst->Org != eOrg->Org ) {
        /* We are merging two disjoint vertices -- destroy eDst->Org */
        joiningVertices = TRUE;
        KillVertex( mesh, eDst->Org, eOrg->Org );
    }
    if( eDst->Lface != eOrg->Lface ) {
        /* We are connecting two disjoint loops -- destroy eDst->Lface */
        joiningLoops = TRUE;
        KillFace( mesh, eDst->Lface, eOrg->Lface );
    }

    /* Change the edge structure */
    Splice( eDst, eOrg );

    if( ! joiningVertices ) {
        TESSvertex *newVertex = (TESSvertex*)bucketAlloc( mesh->vertexBucket );
        if (newVertex == NULL) return 0;

        /* We split one vertex into two -- the new vertex is eDst->Org.
        * Make sure the old vertex points to a valid half-edge.
        */
        MakeVertex( newVertex, eDst, eOrg->Org );
        eOrg->Org->anEdge = eOrg;
    }
    if( ! joiningLoops ) {
        TESSface *newFace = (TESSface*)bucketAlloc( mesh->faceBucket );
        if (newFace == NULL) return 0;

        /* We split one loop into two -- the new loop is eDst->Lface.
        * Make sure the old face points to a valid half-edge.
        */
        MakeFace( newFace, eDst, eOrg->Lface );
        eOrg->Lface->anEdge = eOrg;
    }

    return 1;
}


/* tessMeshDelete( eDel ) removes the edge eDel.  There are several cases:
* if (eDel->Lface != eDel->Rface), we join two loops into one; the loop
* eDel->Lface is deleted.  Otherwise, we are splitting one loop into two;
* the newly created loop will contain eDel->Dst.  If the deletion of eDel
* would create isolated vertices, those are deleted as well.
*
* This function could be implemented as two calls to tessMeshSplice
* plus a few calls to memFree, but this would allocate and delete
* unnecessary vertices and faces.
*/
int tessMeshDelete( TESSmesh *mesh, TESShalfEdge *eDel )
{
    TESShalfEdge *eDelSym = eDel->Sym;
    int joiningLoops = FALSE;

    /* First step: disconnect the origin vertex eDel->Org.  We make all
    * changes to get a consistent mesh in this "intermediate" state.
    */
    if( eDel->Lface != eDel->Rface ) {
        /* We are joining two loops into one -- remove the left face */
        joiningLoops = TRUE;
        KillFace( mesh, eDel->Lface, eDel->Rface );
    }

    if( eDel->Onext == eDel ) {
        KillVertex( mesh, eDel->Org, NULL );
    } else {
        /* Make sure that eDel->Org and eDel->Rface point to valid half-edges */
        eDel->Rface->anEdge = eDel->Oprev;
        eDel->Org->anEdge = eDel->Onext;

        Splice( eDel, eDel->Oprev );
        if( ! joiningLoops ) {
            TESSface *newFace= (TESSface*)bucketAlloc( mesh->faceBucket );
            if (newFace == NULL) return 0;

            /* We are splitting one loop into two -- create a new loop for eDel. */
            MakeFace( newFace, eDel, eDel->Lface );
        }
    }

    /* Claim: the mesh is now in a consistent state, except that eDel->Org
    * may have been deleted.  Now we disconnect eDel->Dst.
    */
    if( eDelSym->Onext == eDelSym ) {
        KillVertex( mesh, eDelSym->Org, NULL );
        KillFace( mesh, eDelSym->Lface, NULL );
    } else {
        /* Make sure that eDel->Dst and eDel->Lface point to valid half-edges */
        eDel->Lface->anEdge = eDelSym->Oprev;
        eDelSym->Org->anEdge = eDelSym->Onext;
        Splice( eDelSym, eDelSym->Oprev );
    }

    /* Any isolated vertices or faces have already been freed. */
    KillEdge( mesh, eDel );

    return 1;
}


/******************** Other Edge Operations **********************/

/* All these routines can be implemented with the basic edge
* operations above.  They are provided for convenience and efficiency.
*/


/* tessMeshAddEdgeVertex( eOrg ) creates a new edge eNew such that
* eNew == eOrg->Lnext, and eNew->Dst is a newly created vertex.
* eOrg and eNew will have the same left face.
*/
TESShalfEdge *tessMeshAddEdgeVertex( TESSmesh *mesh, TESShalfEdge *eOrg )
{
    TESShalfEdge *eNewSym;
    TESShalfEdge *eNew = MakeEdge( mesh, eOrg );
    if (eNew == NULL) return NULL;

    eNewSym = eNew->Sym;

    /* Connect the new edge appropriately */
    Splice( eNew, eOrg->Lnext );

    /* Set the vertex and face information */
    eNew->Org = eOrg->Dst;
    {
        TESSvertex *newVertex= (TESSvertex*)bucketAlloc( mesh->vertexBucket );
        if (newVertex == NULL) return NULL;

        MakeVertex( newVertex, eNewSym, eNew->Org );
    }
    eNew->Lface = eNewSym->Lface = eOrg->Lface;

    return eNew;
}


/* tessMeshSplitEdge( eOrg ) splits eOrg into two edges eOrg and eNew,
* such that eNew == eOrg->Lnext.  The new vertex is eOrg->Dst == eNew->Org.
* eOrg and eNew will have the same left face.
*/
TESShalfEdge *tessMeshSplitEdge( TESSmesh *mesh, TESShalfEdge *eOrg )
{
    TESShalfEdge *eNew;
    TESShalfEdge *tempHalfEdge= tessMeshAddEdgeVertex( mesh, eOrg );
    if (tempHalfEdge == NULL) return NULL;

    eNew = tempHalfEdge->Sym;

    /* Disconnect eOrg from eOrg->Dst and connect it to eNew->Org */
    Splice( eOrg->Sym, eOrg->Sym->Oprev );
    Splice( eOrg->Sym, eNew );

    /* Set the vertex and face information */
    eOrg->Dst = eNew->Org;
    eNew->Dst->anEdge = eNew->Sym;    /* may have pointed to eOrg->Sym */
    eNew->Rface = eOrg->Rface;
    eNew->winding = eOrg->winding;    /* copy old winding information */
    eNew->Sym->winding = eOrg->Sym->winding;

    return eNew;
}


/* tessMeshConnect( eOrg, eDst ) creates a new edge from eOrg->Dst
* to eDst->Org, and returns the corresponding half-edge eNew.
* If eOrg->Lface == eDst->Lface, this splits one loop into two,
* and the newly created loop is eNew->Lface.  Otherwise, two disjoint
* loops are merged into one, and the loop eDst->Lface is destroyed.
*
* If (eOrg == eDst), the new face will have only two edges.
* If (eOrg->Lnext == eDst), the old face is reduced to a single edge.
* If (eOrg->Lnext->Lnext == eDst), the old face is reduced to two edges.
*/
TESShalfEdge *tessMeshConnect( TESSmesh *mesh, TESShalfEdge *eOrg, TESShalfEdge *eDst )
{
    TESShalfEdge *eNewSym;
    int joiningLoops = FALSE;
    TESShalfEdge *eNew = MakeEdge( mesh, eOrg );
    if (eNew == NULL) return NULL;

    eNewSym = eNew->Sym;

    if( eDst->Lface != eOrg->Lface ) {
        /* We are connecting two disjoint loops -- destroy eDst->Lface */
        joiningLoops = TRUE;
        KillFace( mesh, eDst->Lface, eOrg->Lface );
    }

    /* Connect the new edge appropriately */
    Splice( eNew, eOrg->Lnext );
    Splice( eNewSym, eDst );

    /* Set the vertex and face information */
    eNew->Org = eOrg->Dst;
    eNewSym->Org = eDst->Org;
    eNew->Lface = eNewSym->Lface = eOrg->Lface;

    /* Make sure the old face points to a valid half-edge */
    eOrg->Lface->anEdge = eNewSym;

    if( ! joiningLoops ) {
        TESSface *newFace= (TESSface*)bucketAlloc( mesh->faceBucket );
        if (newFace == NULL) return NULL;

        /* We split one loop into two -- the new loop is eNew->Lface */
        MakeFace( newFace, eNew, eOrg->Lface );
    }
    return eNew;
}


/******************** Other Operations **********************/

/* tessMeshZapFace( fZap ) destroys a face and removes it from the
* global face list.  All edges of fZap will have a NULL pointer as their
* left face.  Any edges which also have a NULL pointer as their right face
* are deleted entirely (along with any isolated vertices this produces).
* An entire mesh can be deleted by zapping its faces, one at a time,
* in any order.  Zapped faces cannot be used in further mesh operations!
*/
void tessMeshZapFace( TESSmesh *mesh, TESSface *fZap )
{
    TESShalfEdge *eStart = fZap->anEdge;
    TESShalfEdge *e, *eNext, *eSym;
    TESSface *fPrev, *fNext;

    /* walk around face, deleting edges whose right face is also NULL */
    eNext = eStart->Lnext;
    do {
        e = eNext;
        eNext = e->Lnext;

        e->Lface = NULL;
        if( e->Rface == NULL ) {
            /* delete the edge -- see TESSmeshDelete above */

            if( e->Onext == e ) {
                KillVertex( mesh, e->Org, NULL );
            } else {
                /* Make sure that e->Org points to a valid half-edge */
                e->Org->anEdge = e->Onext;
                Splice( e, e->Oprev );
            }
            eSym = e->Sym;
            if( eSym->Onext == eSym ) {
                KillVertex( mesh, eSym->Org, NULL );
            } else {
                /* Make sure that eSym->Org points to a valid half-edge */
                eSym->Org->anEdge = eSym->Onext;
                Splice( eSym, eSym->Oprev );
            }
            KillEdge( mesh, e );
        }
    } while( e != eStart );

    /* delete from circular doubly-linked list */
    fPrev = fZap->prev;
    fNext = fZap->next;
    fNext->prev = fPrev;
    fPrev->next = fNext;

    bucketFree( mesh->faceBucket, fZap );
}


/* tessMeshNewMesh() creates a new mesh with no edges, no vertices,
* and no loops (what we usually call a "face").
*/
TESSmesh *tessMeshNewMesh( TESSalloc* alloc )
{
    TESSvertex *v;
    TESSface *f;
    TESShalfEdge *e;
    TESShalfEdge *eSym;
    TESSmesh *mesh = (TESSmesh *)alloc->memalloc( alloc->userData, sizeof( TESSmesh ));
    if (mesh == NULL) {
        return NULL;
    }

    if (alloc->meshEdgeBucketSize < 16)
        alloc->meshEdgeBucketSize = 16;
    if (alloc->meshEdgeBucketSize > 4096)
        alloc->meshEdgeBucketSize = 4096;

    if (alloc->meshVertexBucketSize < 16)
        alloc->meshVertexBucketSize = 16;
    if (alloc->meshVertexBucketSize > 4096)
        alloc->meshVertexBucketSize = 4096;

    if (alloc->meshFaceBucketSize < 16)
        alloc->meshFaceBucketSize = 16;
    if (alloc->meshFaceBucketSize > 4096)
        alloc->meshFaceBucketSize = 4096;

    mesh->edgeBucket = createBucketAlloc( alloc, "Mesh Edges", sizeof(EdgePair), alloc->meshEdgeBucketSize );
    mesh->vertexBucket = createBucketAlloc( alloc, "Mesh Vertices", sizeof(TESSvertex), alloc->meshVertexBucketSize );
    mesh->faceBucket = createBucketAlloc( alloc, "Mesh Faces", sizeof(TESSface), alloc->meshFaceBucketSize );

    v = &mesh->vHead;
    f = &mesh->fHead;
    e = &mesh->eHead;
    eSym = &mesh->eHeadSym;

    v->next = v->prev = v;
    v->anEdge = NULL;

    f->next = f->prev = f;
    f->anEdge = NULL;
    f->trail = NULL;
    f->marked = FALSE;
    f->inside = FALSE;

    e->next = e;
    e->Sym = eSym;
    e->Onext = NULL;
    e->Lnext = NULL;
    e->Org = NULL;
    e->Lface = NULL;
    e->winding = 0;
    e->activeRegion = NULL;

    eSym->next = eSym;
    eSym->Sym = e;
    eSym->Onext = NULL;
    eSym->Lnext = NULL;
    eSym->Org = NULL;
    eSym->Lface = NULL;
    eSym->winding = 0;
    eSym->activeRegion = NULL;

    return mesh;
}


/* tessMeshUnion( mesh1, mesh2 ) forms the union of all structures in
* both meshes, and returns the new mesh (the old meshes are destroyed).
*/
TESSmesh *tessMeshUnion( TESSalloc* alloc, TESSmesh *mesh1, TESSmesh *mesh2 )
{
    TESSface *f1 = &mesh1->fHead;
    TESSvertex *v1 = &mesh1->vHead;
    TESShalfEdge *e1 = &mesh1->eHead;
    TESSface *f2 = &mesh2->fHead;
    TESSvertex *v2 = &mesh2->vHead;
    TESShalfEdge *e2 = &mesh2->eHead;

    /* Add the faces, vertices, and edges of mesh2 to those of mesh1 */
    if( f2->next != f2 ) {
        f1->prev->next = f2->next;
        f2->next->prev = f1->prev;
        f2->prev->next = f1;
        f1->prev = f2->prev;
    }

    if( v2->next != v2 ) {
        v1->prev->next = v2->next;
        v2->next->prev = v1->prev;
        v2->prev->next = v1;
        v1->prev = v2->prev;
    }

    if( e2->next != e2 ) {
        e1->Sym->next->Sym->next = e2->next;
        e2->next->Sym->next = e1->Sym->next;
        e2->Sym->next->Sym->next = e1;
        e1->Sym->next = e2->Sym->next;
    }

    alloc->memfree( alloc->userData, mesh2 );
    return mesh1;
}


static int CountFaceVerts( TESSface *f )
{
    TESShalfEdge *eCur = f->anEdge;
    int n = 0;
    do
    {
        n++;
        eCur = eCur->Lnext;
    }
    while (eCur != f->anEdge);
    return n;
}

int tessMeshMergeConvexFaces( TESSmesh *mesh, int maxVertsPerFace )
{
    TESSface *f;
    TESShalfEdge *eCur, *eNext, *eSym;
    TESSvertex *vStart;
    int curNv, symNv;

    for( f = mesh->fHead.next; f != &mesh->fHead; f = f->next )
    {
        // Skip faces which are outside the result.
        if( !f->inside )
            continue;

        eCur = f->anEdge;
        vStart = eCur->Org;

        while (1)
        {
            eNext = eCur->Lnext;
            eSym = eCur->Sym;

            // Try to merge if the neighbour face is valid.
            if( eSym && eSym->Lface && eSym->Lface->inside )
            {
                // Try to merge the neighbour faces if the resulting polygons
                // does not exceed maximum number of vertices.
                curNv = CountFaceVerts( f );
                symNv = CountFaceVerts( eSym->Lface );
                if( (curNv+symNv-2) <= maxVertsPerFace )
                {
                    // Merge if the resulting poly is convex.
                    if( VertCCW( eCur->Lprev->Org, eCur->Org, eSym->Lnext->Lnext->Org ) &&
                        VertCCW( eSym->Lprev->Org, eSym->Org, eCur->Lnext->Lnext->Org ) )
                    {
                        eNext = eSym->Lnext;
                        if( !tessMeshDelete( mesh, eSym ) )
                            return 0;
                        eCur = 0;
                    }
                }
            }

            if( eCur && eCur->Lnext->Org == vStart )
                break;

            // Continue to next edge.
            eCur = eNext;
        }
    }

    return 1;
}


#ifdef DELETE_BY_ZAPPING

/* tessMeshDeleteMesh( mesh ) will free all storage for any valid mesh.
*/
void tessMeshDeleteMesh( TESSalloc* alloc, TESSmesh *mesh )
{
    TESSface *fHead = &mesh->fHead;

    while( fHead->next != fHead ) {
        tessMeshZapFace( fHead->next );
    }
    if( mesh->vHead.next != &mesh->vHead ){
        return;
    }

    alloc->memfree( alloc->userData, mesh );
}

#else

/* tessMeshDeleteMesh( mesh ) will free all storage for any valid mesh.
*/
void tessMeshDeleteMesh( TESSalloc* alloc, TESSmesh *mesh )
{
    deleteBucketAlloc(mesh->edgeBucket);
    deleteBucketAlloc(mesh->vertexBucket);
    deleteBucketAlloc(mesh->faceBucket);

    alloc->memfree( alloc->userData, mesh );
}

#endif

#ifndef NDEBUG

/* tessMeshCheckMesh( mesh ) checks a mesh for self-consistency.
*/
void tessMeshCheckMesh( TESSmesh *mesh )
{
    TESSface *fHead = &mesh->fHead;
    TESSvertex *vHead = &mesh->vHead;
    TESShalfEdge *eHead = &mesh->eHead;
    TESSface *f, *fPrev;
    TESSvertex *v, *vPrev;
    TESShalfEdge *e, *ePrev;

    fPrev = fHead;
    for( fPrev = fHead ; (f = fPrev->next) != fHead; fPrev = f) {
        assert( f->prev == fPrev );
        e = f->anEdge;
        do {
            assert( e->Sym != e );
            assert( e->Sym->Sym == e );
            assert( e->Lnext->Onext->Sym == e );
            assert( e->Onext->Sym->Lnext == e );
            assert( e->Lface == f );
            e = e->Lnext;
        } while( e != f->anEdge );
    }
    assert( f->prev == fPrev && f->anEdge == NULL );

    vPrev = vHead;
    for( vPrev = vHead ; (v = vPrev->next) != vHead; vPrev = v) {
        assert( v->prev == vPrev );
        e = v->anEdge;
        do {
            assert( e->Sym != e );
            assert( e->Sym->Sym == e );
            assert( e->Lnext->Onext->Sym == e );
            assert( e->Onext->Sym->Lnext == e );
            assert( e->Org == v );
            e = e->Onext;
        } while( e != v->anEdge );
    }
    assert( v->prev == vPrev && v->anEdge == NULL );

    ePrev = eHead;
    for( ePrev = eHead ; (e = ePrev->next) != eHead; ePrev = e) {
        assert( e->Sym->next == ePrev->Sym );
        assert( e->Sym != e );
        assert( e->Sym->Sym == e );
        assert( e->Org != NULL );
        assert( e->Dst != NULL );
        assert( e->Lnext->Onext->Sym == e );
        assert( e->Onext->Sym->Lnext == e );
    }
    assert( e->Sym->next == ePrev->Sym
        && e->Sym == &mesh->eHeadSym
        && e->Sym->Sym == e
        && e->Org == NULL && e->Dst == NULL
        && e->Lface == NULL && e->Rface == NULL );
}

#endif
